The present invention relates to hinge mechanisms for vehicle seats, and to seats fitted with such mechanisms.
More particularly, the invention relates to a hinge mechanism for a vehicle seat to adjust the inclination of a seat back relative to a seat proper about a pivot axis, the mechanism comprising:
first and second rigid strength members mounted to pivot relative to each other about the pivot axis, one of these strength members being for connection to the seat back and the other one for connection to the seat proper;
a set of teeth secured to the first strength member and forming at least one circular arc centered on the pivot axis;
at least two toothed slugs mounted on the second strength member and movable at least radially relative to the pivot axis between a locking position in which each slug co-operates with the set of teeth to prevent the first and second strength members moving relative to each other, and a retracted position in which each slug does not interfere with the set of teeth;
a control device mounted to pivot about the pivot axis and adapted to provide positive control over the displacement of each slug from its locked position to its retracted position, and vice versa; and
an at least partially-circular stepped ramp secured to the first strength member, said ramp having an unlocking angular sector for co-operating with a control slug and for holding the control slug in its retracted position, and a locking angular sector in which the ramp does not interfere with the control slug.
With hinge mechanisms of this type, the seat back cannot pivot while the mechanism is locked, i.e. so long as the control device has not moved the slugs into their retracted position. However, once the slugs have been moved into the retracted position by means of the control device, then the ramp enables the hinge mechanism to be maintained in the unlocked state, even after the control member has been released, during certain maneuvers of the seat back such as being folded down forwards temporarily in order to give access to the back seat of the vehicle.
Document EP-B-0 770 514 describes an example of such a mechanism, which mechanism gives full satisfaction.
That mechanism has three slugs that are regularly distributed around the pivot axis in order to balance the hinge mechanism, in particular in reaction to radial forces exerted on the pivot axis, and the ramp co-operates with each slug in order to maintain them in the retracted position. The ramp thus has three locking angular sectors and three unlocking angular sectors. The sum of the locking and unlocking angular sectors for a single slug is thus equal to 120xc2x0 and the tilting range of the seat back cannot exceed that value.
A particular object of the present invention is to further increase the tilting range of the seat back, for example in order to tilt the seat back forwards in order to gain access to the back seat, and backwards into a reclining or bunk position.
To this end, according to the invention, in a hinge mechanism of the kind in question, the angular sum of the locking and unlocking angular sectors, for the control slug able to co-operate with the ramp, extends over more than 120xc2x0 about the pivot axis.
By means of these dispositions, the seat back can pivot over at least 120xc2x0, for example, between an in-use position in which it extends substantially vertically and a forward position facilitating access to the back seats of the vehicle and/or between said in-use position and a bunk or reclining position in which the seat back extends towards the back of the vehicle substantially parallel to the seat proper and/or between the bunk position and the position that facilitates access to the back seat.
In preferred embodiments of the invention, recourse may optionally also be made to one or more of the following dispositions:
the mechanism has only one control slug, each other slug being an auxiliary slug shaped so as not to co-operate with the ramp;
the locking angular sector extends about the pivot axis over 30xc2x0 to 90xc2x0, with the unlocking angular sector being complementary to the locking angular sector to make up 360xc2x0;
the locking angular sector extends about the pivot axis substantially over 60xc2x0, the unlocking angular sector being complementary to the locking angular sector to make up 360xc2x0;
the control slug has a peg extending parallel to the pivot axis, adapted to co-operate with the ramp when the unlocking angular sector is in register with the control slug;
the control device comprises a rotary cam urged resiliently between a rest position in which it holds each slug in co-operation with the set of teeth, and an active position in which it does not co-operate with the slugs;
the control device has a mask which is secured to the cam and which overlies each slug at least in part, said mask having cutouts adapted to co-operate with projecting pegs formed on one surface of each slug situated facing said mask, so as to move the slugs simultaneously towards their retracted positions when the cam is moved towards its active position;
the control slug for co-operating with the ramp is adapted to lock the cam in its active position while it is being held by the ramp, when in the retracted position;
the mechanism has two auxiliary slugs placed at substantially 120xc2x0 to the control slug, and the second strength member has two reaction bearings projecting from its face facing the slugs, each of the reaction bearings being situated respectively between two slugs and being adapted to co-operate in sliding contact with the cam via a surface extending over a circular arc about the pivot axis; and
the cam has an abutment extending between two slugs and adapted to block displacement of the control device in an angular sector defined by two counter-abutments projecting from the surface of the second strength member facing the cam and corresponding respectively to the rest position and to the active position of the cam.
In another aspect, the invention provides a vehicle seat including a seat back pivotally mounted on a seat proper by means of at least one hinge mechanism as defined above.